Betacoronavirus

VIRION

Enveloped, spherical, about 120 nm in diameter. The RNA genome is associated with the N protein to form the nucleocapsid. see Neuman BW et al. for virion cryo-electron microscopy analysis.

GENOME

Monopartite, linear ssRNA(+) genome of 27-32kb in size (the largest of all RNA virus genomes). Capped, and polyadenylated. The leader RNA (65-89 bp) at the 5’ end of the genome is also present at the end of each subgenomic RNAs.

GENE EXPRESSION

The virion RNA is infectious and serves as both the genome and viral messenger RNA. Genomic RNA encodes ORF1a, as for ORF1b, it is translated by ribosomal frameshifting. Resulting polyproteins pp1a and pp1ab are processed into the viral polymerase (RdRp) and other non-structural proteins involved in RNA synthesis. Structural proteins are expressed as subgenomic RNAs. Each RNA (genomic and subgenomic) is translated to yield only the protein encoded by the 5’-most ORF.